Smooth growth is not easy even for adult livestock, and more difficult for young livestock which is inferior in physical strength and more delicate. For example, in the case of newborn calves, growth-inhibitory factor include insufficient intake of colostrum, inadequate (unsanitary) environment, change in feed, change from mother's milk to artificial feed (substitute milk, starter, or the like), and stress due to transportation or change in breeding environment.
In the intestine of a healthy animal, certain intestinal normal inhabitants existing on the intestinal mucosal epithelia prevent the infections with various pathogenic bacteria. On the other hand, the intestinal flora loses its balance by a change in diet, stress or administration of an antibiotic. It has been reported that a decrease of either one of Lactobacillus or Bifidobacterium was observed in calves suffering from diarrhea, and it has been pointed out that these beneficial bacteria are important.
Major diseases of calves are digestive diseases having diarrhea as a main symptom and respiratory diseases having pneumonia as a main symptom. Diarrhea appears within two weeks after the introduction, followed by the respiratory diseases. Calves lose their passive antibodies two or three weeks after birth and the calves themselves start production of antibodies on and after four weeks after birth. Infectious diseases of calves due to IgG insufficiency include, for example, diarrhea caused by Escherichia coli, rotavirus, coronavirus, Cryptosporidium or Salmonella. It has been reported that group of calves having a high incidence of pneumonia suffered from diarrhea or malnutrition after birth and are recognized to have depressed thymus-derived cell function during one month after birth which is an important period for the maturation of lymphocytes.
Since calves have a remarkably high morbidity and mortality thereof often exceeds 5%, and it has been a disincentive for management.
Accordingly, antibiotics have come to be used in this industry. Administration of antibiotics (colistin sulfate and bacitracin zinc) to calves is permitted, for example, in Japan. However, it is socially desired not to use antibiotics in view of prevention of appearance of resistant bacteria thereto. However, in practice, antibiotics are frequently used for promoting growth of calves. In Japan, there is a tendency to legally prohibit the use of antibiotics. Therefore, in this industry, there is a demand for the development of a feed additive composition which can be used safely as a substitute for antibiotics.
As the growth promoters for calves other than antibiotics, the followings are commercially available at present. However, none of the followings are found to be superior in effect to antibiotics permitted at present.
(1) Probiotics (Enterococcus faecalis, Enterococcus faecium, Clostrdium butyricum, Bacillus subtilis, Bacillus cereus, Bifidobacterium thermophilum, Bifidobacterium pseudolongum, Lactobacillus acidophilus)
(2) Oligosaccharides
(3) β-carotene
(4) Vitamin C
(5) Herb (oregano) extract
(6) Yeast cell-wall constituent (glucomannan), yeast cell-membrane constituent (β-glucan)
With regards to probiotics, administration of a residue of culture of Bifidobacterium adolescentis ATCC 15703 to calves in combination with an antibiotic has been proposed and the effect on weight gain has been investigated. However, this proposal is based on the use in combination with the antibiotic, and single use of the above bifidobacterium is not included (refer to, for example, JP-A-62-104552).
With regards to Lactobacillus acidophilus, there is a report on the administration of L. acidophilus to calves, but satisfactory results have not been obtained yet. In addition, although a probiotic of L. acidophilus is commercially available, it is not composed of L. acidophilus alone but a mixture with another bacterium. In 1980, re-classification of L. acidophilus into 6 sub-groups (L. acidophilus, L. crispatus, L. amylovorus, L. gallinarum, L. gasseri, and L. johnsonii) was proposed according to the homology of a chromosomal DNA possessed by the bacterium and sugar composition analysis of cell wall constituents. Since it is not clear to which sub-group of the 6 sub-groups the L. acidiphilus which has not been classified by the above-described identification method belongs, it is impossible to identify the kind of bacterium.
Lactic acid bacteria belonging to Lactobacillus gasseri and substances containing the same have been found to have an inhibiting activity against Helicobacter pylori (which may hereinafter be called H. pylori) which is a cause of gastric ulcer and is pointed out to have a relation to gastric cancer (refer to, for example, Japanese Patent No. 3046303). However, it has not been known that the bacterium body of L. gasseri, culture thereof, or residue of culture which is obtained by separating and removing solid matters from the culture has an intestinal flora-improving activity, an anti-diarrhea activity, an antioxidant activity and a weight-increasing activity for young livestock such as calves.